As a discipline, probability theory has been brewing for more than 200 years around16th century, and it came into being around the middle of17th century. The main reasons were the emergence and development of insurance industry and the prevalence of gambling. The prevalence of gambling provides an excellent model for the study of probability theory (for example, the equal probability of rolling dice is obvious and can be used for repeated experiments), which plays a catalytic role in probability theory.
Probability theory is a branch of mathematics that studies the quantitative laws of random phenomena. Random phenomenon is relative to decisive phenomenon, and the inevitable occurrence of a certain result under certain conditions is called decisive phenomenon. For example, at standard atmospheric pressure, when pure water is heated to 100℃, water will inevitably boil. Random phenomenon means that under the same basic conditions, before each experiment or observation, it is uncertain what kind of results will appear, showing contingency. For example, when you flip a coin, there may be heads or tails. The realization and observation of random phenomena are called random experiments. Every possible result of random test is called a basic event, and a basic event or a group of basic events is collectively called a random event, or simply called an event. Typical random experiments include dice, coins, playing cards and roulette.
The probability of an event is a measure of the possibility of an event. Although the occurrence of an event in random trials is accidental, those random trials that can be repeated in large numbers under the same conditions often show obvious quantitative laws.